1. Field of the Invention
The present invention relates to a solid-state image capturing apparatus and an electronic information device, and more particularly to a solid-state image capturing apparatus, such as a CMOS image sensor, configured with semiconductor elements, for performing a photoelectric conversion on and capturing an image light from a subject; and an electronic information device including the solid-state image capturing apparatus as an image input device used in an image capturing section thereof.
2. Description of the Related Art
Recently, a CMOS image sensor can be produced by a semiconductor forming process, which is a general CMOS process, and therefore, attention is riveted to such a CMOS image sensor as a solid-state image capturing apparatus that can be provided at a low price. However, there is a problem of noise even with such a CMOS image sensor.
Regarding the noise, there exists a fixed noise, which occurs always at the same pixel (at the same position on a screen) regardless of a photographing timing, and random noise (Random Telegraph Signal Noise), which occurs at a different pixel (at a different position on a screen) depending on a photographing timing.
Such random noise is a result of crystal defect that exists at a readout path of a signal charge and an interface level, and particularly is caused when an electric charge is captured at a silicon/gate insulation film interface of a source follower transistor. Therefore the random noise decides a noise level of a recent solid-state image capturing apparatus in which a pixel size is reduced to several times the size of a wavelength of light.
The reduction of the random noise is especially requested currently in order to obtain a fine and highly sensitive image without the presence of noise under a condition of low luminous intensity. For example, Reference 1 discloses a technique to reduce the random noise.
Reference 1 describes a technique where a gate insulation film of a transistor inside a pixel that configure a solid-state image capturing apparatus is formed such that at least a portion near a silicon interface is composed of an oxide that does not include nitrogen so that misfitting of a crystal lattice derived from nitrogen atoms is eliminated, thereby reducing the defect level density of the silicon/gate insulation film interface to control the occurrence of the random noise.
Reference 1: Japanese Laid-Open Publication No. 2006-313899